Retinal ganglion cell depletion alters the phenotypic expression of GABA and GAD in the rat retina

Segmented retinal layer analysis of chiasmal compressive optic neuropathy in pituitary adenoma patients

AIMS

To evaluate changes in the segmented retinal layers of pituitary adenoma (PA) patients and to identify the relationship between these changes and visual function.

METHODS

A total of 47 (PA patients) and 22 (healthy subjects) eyes were reviewed from the medical records. The PA patients performed a visual field (VF) test before surgery and 1 month after surgery. By optical coherence tomography scanning, eight retinal layers were measured: retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer, outer nuclear layer, retinal pigment epithelium, and photoreceptor layer.

RESULTS

The PA group showed reduced RNFL, GCL, and IPL thicknesses (p = 0.004,< 0.001,< 0.001) and thicker INL thickness (p = 0.012) than did the controls. The mean deviation of preoperative VF in the PA group was positively correlated with RNFL, GCL, and IPL thicknesses (R = 0.664, 0.720, 0.664; p < 0.001,< 0.001,< 0.001) and negatively correlated with the INL thickness (R = -0.400; p = 0.010). Among the 47 eyes, 32 eyes (68%) were included for subgroup analysis. Preoperative RNFL, GCL, and IPL thicknesses were thicker in the postoperatively improved VF group (p = 0.019, 0.009, 0.005). The preoperative cutoff values for visual recovery were 23.6 μm for RNFL thickness, 30.6 μm for GCL thickness, and 28.9 μm for IPL thickness.

CONCLUSION

During chiasmal compression, the thickening of the INL has presented in addition to thinning of the inner retinal layers. Also, changes in retinal anatomical structures are related to the extent of VF defect and can be used as a predictor of postoperative visual recovery.

The effects of immune protein CD3ζ development and degeneration of retinal neurons after optic nerve injury

Major histocompatibility complex (MHC) class I molecules and their receptors play fundamental roles in neuronal death during diseases. T-cell receptors (TCR) function as MHCI receptor on T-cells and both MHCI and a key component of TCR, CD3ζ, are expressed by mouse retinal ganglion cells (RGCs) and displaced amacrine cells. Mutation of these molecules compromises the development of RGCs. We investigated whether CD3ζ regulates the development and degeneration of amacrine cells after RGC death. Surprisingly, mutation of CD3ζ not only impairs the proper development of amacrine cells expressing CD3ζ but also those not expressing CD3ζ. In contrast to effects of MHCI and its receptor, PirB, on other neurons, mutation of CD3ζ has no effect on RGC death and starburst amacrine cells degeneration after optic nerve crush. Thus, unlike MHCI and PirB, CD3ζ regulates the development of RGCs and amacrine cells but not their degeneration after optic nerve crush.

GABA and GABA receptors alterations in the primary visual cortex of concave lens-induced myopic model

Until recently most researches on myopia mechanisms have mainly been focused on the eye ball and few investigations were explored on the upper visual pathway, such as the visual cortex. The roles of gamma-aminobutyric acid (GABA) in the retinal and in the upper visual pathway are inter-correlated. As the retinal glutamate decarboxylase (GAD), GABA, and the mRNA levels of GABA receptors increased during the concave lens induced myopia formation, however, whether GABA alterations also occurred in the visual cortex during the concave lens induction is still unknown. In the present study, using HPLC, Enzyme-Linked Immunosorbent Assay (ELISA) and Real-Time Quantitative-PCR (RT-PCR) methods, we observed the changing trends of GABA, glutamate decarboxylase (GAD), and GABA receptors in the visual cortex of concave lens-induced myopic guinea pigs. Similar to the changing patterns of retinal GABA, the concentrations of GAD, GABA and the mRNA levels of GABA receptors in the visual cortex also increased. These results indicate that the exploration on myopia mechanisms should possibly be investigated on the whole visual pathway and the detailed significance of cortical GABA alterations needs further investigation.

Outer retinal changes following acute optic neuritis

BACKGROUND

Retinal nerve fiber and ganglion cell+inner plexiform (GCIP) layer thinning following multiple sclerosis-related acute optic neuritis (AON) is well described. However, whether AON results in changes in the inner nuclear (INL), outer plexiform (OPL), outer nuclear (ONL) and/or photoreceptor segment (PS) layers remains undetermined.

OBJECTIVES

The objective of this paper is to determine if INL+OPL and/or ONL+PS changes occur following AON.

METHODS

Thirty-three AON patients underwent serial optical coherence tomography (OCT) and visual function testing (mean follow-up: 25 months). Longitudinal changes in retinal layer thickness were analyzed using mixed-effects linear regression.

RESULTS

Four months following AON, the mean decrease in GCIP thickness relative to baseline was 11.4% (p < 0.001). At four months, a concomitant 3.4% increase in average ONL+PS thickness was observed (p < 0.001). The percentage decrease in GCIP thickness and increase in ONL+PS thickness were strongly correlated (r = -0.70; p < 0.001). Between months 4 to 12, ONL+PS thickness declined and, at 12 months, was no longer significantly different from baseline (mean change: 0.5%; p = 0.37). Similar, albeit less robust, changes in the INL+OPL were observed.

CONCLUSIONS

Following AON, dynamic changes occur in the deep retinal layers, which are proportional to GCIP thinning. These novel findings help further our understanding of the biological and/or anatomical sequelae resulting from AON.

Flash electroretinography and pattern visual evoked potential changes in ocular hypertension patients

Purpose. To evaluate the changes of flash electroretinography (fERG) and pattern visual evoked potentials (pVEP) in ocular hypertension (OHT) patients. Methods. Twenty-five OHT patients and 30 healthy volunteers were enrolled for this cross-sectional study. Opthalmologic examinations, visual field tests, pVEP and fERG were performed. The main outcome measures were the differences between pVEP and fERG parameters. Results. The mean age of OHT patients and volunteers were 57 ± 12.25 years (range 30-65 years), and 53.25 ± 12.0 years (range 30-65 years), respectively. The mean amplitude of the pVEP was statistically lower in the OHT group (P < 0.05). Latency of the two groups was different; however, the difference was not statistically significant (P > 0.05). In fERG of OHT group, there was a significant decrease in the amplitude of the oscillatory potentials (Ops), and a significant delay in latency of rod and cone waves (all P < 0.05). There was no significant change in the flicker fERG waves between the two groups (P > 0.05). Conclusions. Although we found a decrease in Ops amplitude and a prolonged latency in flicker fERG, only the decrease in Ops amplitude was statistically significant between the two groups. The amplitude of Ops wave and amplitude of pVEP may reflect early glaucomatous damage in OHT patients.

Impact of ethanol on the developing GABAergic system

Alcohol intake during pregnancy has a tremendous impact on the developing brain. Embryonic and early postnatal alcohol exposures have been investigated experimentally to elucidate the fetal alcohol spectrum disorders' (FASD) milieu, and new data have emerged to support a devastating effect on the GABAergic system in the adult and developing nervous system. GABA is a predominantly inhibitory neurotransmitter that during development excites neurons and orchestrates several developmental processes such as proliferation, migration, differentiation, and synaptogenesis. This review summarizes and brings new data on neurodevelopmental aspects of the GABAergic system with FASD in experimental telencephalic models.

The effect of experimental glaucoma and optic nerve transection on amacrine cells in the rat retina

PURPOSE

To detect alterations in amacrine cells associated with retinal ganglion cell (RGC) depletion caused by experimental optic nerve transection and glaucoma.

METHODS

Intraocular pressure (IOP) was elevated unilaterally in 18 rats by translimbal trabecular laser treatment, and eyes were studied at 1 (n = 6), 2 (n = 5), and 3 (n = 7) months. Complete optic nerve transection was performed unilaterally in nine rats with survival for 1 (n = 4) and 3 (n = 5) months. Serial cryosections (five per eye) were immunohistochemically labeled with rabbit anti-gamma-aminobutyric acid (GABA) and anti-glycine antibodies. Cells in the ganglion cell and inner nuclear layers that labeled for GABA or glycine were counted in a masked fashion under bright-field microscopy. Additional labeling with other RGC and amacrine antigens was also performed. RGC loss was quantified by axon counts.

RESULTS

Amacrine cells identified by GABA and glycine labeling were not significantly affected by experimental glaucoma, with a mean decrease of 15% compared with bilaterally untreated control cells (557 +/- 186 neurons/mm [glaucoma] versus 653.9 +/- 114.4 neurons/mm [control] of retina; P = 0.15, t-test). There was no significant trend for amacrine cell counts to be lower in eyes with fewer RGCs (r = -0.39, P = 0.11). By contrast, there was highly significant loss of GABA and glycine staining 3 months after nerve transection, both in the treated and the fellow eyes (P < 0.0001, t-test). However, there was a substantial number of remaining amacrine cells in transected retinas, as indicated by labeling for calretinin and calbindin.

CONCLUSIONS

Experimental glaucoma causes minimal change in amacrine cells and their expression of neurotransmitters. After nerve transection, neurotransmitter presence declines, but many amacrine cell bodies remain. Differences among optic nerve injury models, as well as effects on "untreated" fellow eyes, should be recognized.

Structural changes in the developing retina maintained in vitro

The present study examined the emergence of structural remodeling in explanted neonatal rat retina. Immunohistochemical analysis demonstrated signs of glial and neuronal remodeling after 11 days in vitro and included the activation of Müller cells, the formation of ectopic neuropil areas and sprouting of photoreceptor terminals. We also observed that cholinergic and GABA-ergic amacrine cells displayed signs of disorganized laminations. These results demonstrate that retinal culturing initiates structural changes that show morphological similarities to glial and neuronal remodeling identified in retinitis pigmentosa retinas and experimentally detached retinas.

Rabbit retinal ganglion cell survival after optic nerve section and its effect on the inner plexiform layer

Structural modifications of the inner retina were studied after optic nerve section (ONS) in the rabbit. Retinal ganglion cells (RGC) were labelled by injection of Fast Blue into the optic nerve, and counted under fluorescent light in control retina and retina 7, 14, 21 and 26 days post-axotomy. Studies on retinal cross-sections were also performed. For this purpose, retinal sections were stained with haematoxylin-eosin and immunohystochemistry for alpha1 and beta2/beta3 sub-units of the GABA(A) receptors. One week after axotomy, there was no significant loss in the number of ganglion cells with respect to control counts (1086+/-173cellsmm(-2) in the visual streak and 119+/-46cellsmm(-2) in the periphery, mean+/-SD, n=5). At 14 days post-axotomy, 271+/-46cellsmm(-2) remained in the visual streak and 33+/-6cellsmm(-2) in the periphery, corresponding to a mean survival of 27%. The number of ganglion cells decreased further on the following days, reaching 7.54% 1 month after ONS. A significant reduction in the thickness of the inner plexiform and ganglion cell layers was also observed in retinal cross-sections. Immunocytochemical studies show a remarkable disorganization of the layer stratification in the inner plexiform layer (IPL). We conclude that after ONS, RGC death occurs mainly between 7 and 14 days post-axotomy and a progressive death up to 26 days, causing a decrease in the thickness of the IPL and subsequent disorganization of its layers.

Cell death in the inner nuclear layer of the retina is modulated by BDNF

Developing amacrine cells in the vertebrate retina undergo naturally-occurring cell death which is accentuated by the early removal of retinal ganglion cells. We show that providing BDNF or decreasing endogenous BDNF via competitive binding with soluble TrkB receptors in a whole-retina culture assay modulates the frequency of dying cells in the amacrine cell layer. Ganglion cells synthesize BDNF, and amacrine cells express TrkB receptors, suggesting a likely signaling mechanism.

Two phases of increased cell death in the inner retina following early elimination of the ganglion cell population

Neurons in the inner nuclear layer (INL) of the vertebrate retina undergo considerable programmed cell death during development, but the determinants of this cell death remain largely unknown. The present study examines the role of retinal ganglion cells in support of INL neurons in the developing ferret retina. The retinal ganglion cell population was eliminated by optic nerve transection at postnatal day (P) 2, and the incidence of cell death was examined using terminal deoxytransferase dUTP nick-end labelling (TUNEL) at various ages during the first 3 postnatal weeks. Significant increases in TUNEL-positive cells were observed in the neuroblast layer (NBL) as early as P3, prior to synapse formation within the inner plexiform layer (IPL), and again in the INL at P22, the normal peak of naturally occurring cell death within the ferret's INL. A decrease in TUNEL-positive cells was found in the NBL at P8. These results show three phases of response to the loss of retinal ganglion cells and suggest that cells in the NBL/INL are normally dependent on retinal ganglion cells for their survival. Recent studies have shown that certain populations of retinal neurons are reduced in adult animals that had lost the population of ganglion cells during early development, so the present study also examined when this reduction could first be detected. The number of parvalbumin-immunoreactive amacrine cells was decreased significantly in the NBL of the manipulated eye as early as P8, when we could first label this population, and this difference persisted through adulthood. The fact that cell death in the NBL has already increased within 24 hours of ganglion cell elimination, coupled with the specificity of this effect on the adult complement of INL cell types, shows that cell-cell interactions controlling survival are already highly specific for particular types of retinal neuron early in development